balls up!!!

[beaver74]

hi all
just realised i've missed some thing
had the chance of having a bit of 10.00mm swa 3core at a good price installed it as the voltdrop is fine over 8M and is fine for the 60A supply but now i have got home checking through regs it is about 10A over when calculating the current rating for the 10mm 3 core clipped dirrect 67A x1.45 which only give me 97.15A.
the fuse is a 1361 60A with a rating of 100+ in the time curves for 1 hr

now i know there is not likely to be full load used on this submain buty surely this circuit can not comply ?

has any body got a nugget of gold to get me out of the smelly stuff

 

[telectrix]

drop the fuse rating? is the cable XLPE?

 

[beaver74]

no standard cicular cores and it a big drop down to 45A

 

[scotsparky]

you factored in temperature,thermals, groupng,ect. remember current rating is worked out at 70 or 90 degrees depending on cable so a 1.2 factor can be used if ambient temop ios 20deg

 

[telectrix]

so's xlpe. it's rated 81A continuous. a lot of the swa is xlpe now. check it.

 

[beaver74]

so's xlpe. it's rated 81A continuous. a lot of the swa is xlpe now. check it.

as in BS 6724 ?
i thought xlpe were the triangular type conductors

 

[telectrix]

nope, it's just higher rated cable 90deg. C. 81A clipped or buried. should say xlpe on the outer sheath. some of the bigger sizes may be triangular but 10mm is round. i used some a few weeks ago. 63AMCB at front end.

 

[dsb electrical]

XLPE = Cross-Linked Polyethelene

There are actually two semi-conductive layers on high voltage cable. One is between the actual conductors and the XLPE. The other semi-con is on outside of the XLPE insulation underneath the concentric neutral.

The semi-con is used to equalize the electrical stresses over a large area. For example, most conductors are made up of multiple strands of copper or aluminum. The outer edge of the conductor bundle is not smooth. It has several ridges on the outer edge where the individual strands meet one another. These high spots will stress the insulation leading to a premature failure. The internal semi-con makes a smooth voltage level for the XLPE where it meets the conductor strands.

if any one wondering what the xple bit was
​

 

[beaver74]

cheers

 

[Engineer54]

XLPE = Cross-Linked Polyethelene

There are actually two semi-conductive layers on high voltage cable. One is between the actual conductors and the XLPE. The other semi-con is on outside of the XLPE insulation underneath the concentric neutral.

The semi-con is used to equalize the electrical stresses over a large area. For example, most conductors are made up of multiple strands of copper or aluminum. The outer edge of the conductor bundle is not smooth. It has several ridges on the outer edge where the individual strands meet one another. These high spots will stress the insulation leading to a premature failure. The internal semi-con makes a smooth voltage level for the XLPE where it meets the conductor strands.

if any one wondering what the xple bit was
​

There isn't a neutral conductor in HV cables, and never seen a concentric HV cable either, ...not for distribution anyway. Normal HV cable will just be the 3 phases. The semi conductive layers is as you describe but on each core. Heat shrink termination packs will remove the outer semi conductive layer before the tails are further insulated....

How come we have moved from L Voltage XLPE SWA cables, to HV cables anyway ?? (should be calling them ''MV'' these days) ...lol!!

 

[Deleted member 9648]

nope, it's just higher rated cable 90deg. C. 81A clipped or buried. should say xlpe on the outer sheath. some of the bigger sizes may be triangular but 10mm is round. i used some a few weeks ago. 63AMCB at front end.

You need to keep in mind that if you fully load xlpe SWA ,in theory it will run @ 90deg. Therefore terminations have to be rated at 90deg....more often than not they wont be. In practice I've never seen any problems here,but a fully loaded xlpe SWA terminated into say a standard CU main swtitch will not comply.

 

[Chr!s]

hi all
just realised i've missed some thing
had the chance of having a bit of 10.00mm swa 3core at a good price installed it as the voltdrop is fine over 8M and is fine for the 60A supply but now i have got home checking through regs it is about 10A over when calculating the current rating for the 10mm 3 core clipped dirrect 67A x1.45 which only give me 97.15A.
the fuse is a 1361 60A with a rating of 100+ in the time curves for 1 hr

now i know there is not likely to be full load used on this submain buty surely this circuit can not comply ?

has any body got a nugget of gold to get me out of the smelly stuff

Beaver, Read reg 433.1.1, you need to comply with parts (i),(ii),(iii)

Now its part (iii) your questioning provided the two other conditions are met.

Now read reg 433.1.2 for your nugget

 

[mechelec]

There isn't a neutral conductor in HV cables, and never seen a concentric HV cable either, ...not for distribution anyway. Normal HV cable will just be the 3 phases. The semi conductive layers is as you describe but on each core. Heat shrink termination packs will remove the outer semi conductive layer before the tails are further insulated....

How come we have moved from L Voltage XLPE SWA cables, to HV cables anyway ?? (should be calling them ''MV'' these days) ...lol!!

The closest you get to concentric MV/HV cable construction is XLPE Triplex cable which has a central conductor surrounded by insulation and semi conductive layers with copper drain earths under the outer sheath

 

[Engineer54]

Yep, that'll be single core MV/HV distribution cable... Bit of a difference though, ...between a neutral conductor and a earthing drain!!....

 

[beaver74]

thanks all

been to job and it is 90 deg
but as noted by ch!ss not a problem and again i have asked a question i know the answer to as i was told of this a wail ago